Encoder Front Page
SRS Home | Front Page | Monthly Issue | Index
Google
Search WWW Search seattlerobotics.org


Tortilla-Board™: A New Breadboard Technique

April, 1998

Kevin Ross

I was working hard one evening, trying desperately to get a project done. The project at hand was a system to log the number of cars that run the local stop sign. Each day around 2:00pm, the local high school lets out, and about half of the driving student body races down our street. It seems like they all run the stop sign. I like to have accurate information to complain with, so I thought I should count the number of cars that didn't appear to stop. I realized that I needed to create a Microcontroller circuit to complete my project.

It was 1:45am when I had the answer to my design. I quickly gather up all of the required parts, and reached into the drawer to find a small section of breadboard. I use a lot of these little circuit boards. Whenever I see a Radio Shack at a mall, I always stop in and purchase the entire stock of 4"x6" predrilled PC boards (Radio Shack #276-147A). Usually, I can find at least one or two on the wall. If not, then there is a strong chance that Karl Lunt has visited the store recently, since he and I seem to clean out the stock of these all around the north end of Lake Washington, which is in the Seattle area.

As luck would have it, I was out of breadboards. At this hour, all of my usual Radio Shack stores were closed, and besides, I had been unable to find any at the last 5 Radio Shacks I had visited.  I thought about calling Karl to ask if I could borrow a couple, but his place is about 40 minutes each way, and it was really late. Then I realized that he was probably the reason I hadn't been able to find any in the area. Out of frustration, I called anyway and hung up after a couple of rings. At least I felt a little better now that we were both awake.

I considered several options for assembling my circuit without a breadboard, but that predrilled board really was a key part to doing this quickly. It was now 2am, and time for an early morning feeding. I raced down the stairs to find a tasty snack. This is where I found the solution to all of my problems. Right there in the second shelf, laying flat beneath the tub of sour cream, was a short stack of 8" flour tortillas. I popped out the last two of the flat uniform sheets, and threw the packaging in the trash. To one I attached a slice of cheese, rolled it into a tight tube, and consumed it in three very large bites. The other was whisked up the stairs to my work room.

At first, I thought this was a truely crazy idea. However, as I started to assemble my circuit, it became apparent that I was on to something. Here are a few comparisons:

  1. A standard breadboard has holes on 100 mil centers. A tortilla has holes wherever you push the pins of the part through. If you have ever tried using a part with a non-rectangular pin layout, such as the LM18200T H-Bridge, you understand what I mean. Standard breadboards are useless on those parts.
  2. A standard breadboard is ridged and flat. The tortilla is soft and plyable. This allows you to create a breadboard, ah, er, Tortilla-Board™ design that conforms to another shape.
  3. A standard breadboard can be difficult to cut. A Tortilla-Board™ can be torn, cut, or downright chewed into whatever shape you desire.

I starting think more and more about this idea, and realized several other benefits to using the Tortilla-Board™ as a develoment system.


Putting It To The Test

It turns out that tortillas are non-conducting, which was my first obvious test. I didn't want to short out everything. I was actually surprised by this, as I would have thought that the moisture in the tortilla might cause a short circuit. Have no fear, the Tortilla-Board™ is electrically safe enough for my purposes. You might need to experiment with higher power circuits, and I make no claims about the safety of using the Tortilla-Board™.

image04.jpg (60667 bytes)

As you can see in the picture, I was able to place parts quickly and easily into the Tortilla-Board™. Use some care in insuring that the leads of your components make a clean hole through the material. If you are having problems pushing the leads through, then you might try warming your Tortilla-Board™ in the microwave for 15 seconds or so. This appears to help. As you can see, I was able to mount several different package types using the Tortilla-Board™, including that pesky LM18200T H-Bridge.

I chose to wire-wrap my board together, only soldering where absolutely necessary. It turns out the natural oils in the Tortilla-Board™ act as a very efficient flux agent, allowing me to use solid core solders. This is evironmentally friendly, and smells very tasty as you solder.

As you can see in the following picture, parts can be arranged in a host of different configurations. I have only partially completed the circuit in the picture, but rest assured the assembly was quick and smelled very good when I was done.

image02.jpg (25600 bytes)

After assembly was complete, I set my Tortilla-Board™ creation in a warm place. After two days, the Tortilla-Board™ became hard. Other experiments have shown that you can shape your Tortilla-Board™ into whatever shape you like. After a couple of days, it will retain that shape. Very handy.


Amazing Things Happen

Once I completed my circuit, I powered it up to make it go. A couple of minor corrections to the address bus, and I was off and running. I carefully programmed the timer section to generate a 40khz pulse, but for some reason I was getting 79khz pulse. It took me the better than 3 hours to determine what was happening. The resonant frequency of the Tortilla-Board™ is a harmonic of the clock frequency. This caused a feedback loop in the oscillator that increase the clock frequency of the 68HC11 by a factor of almost 2. That means that programs written for 68HC11 circuits using the Tortilla-Board™ run twice as fast. That was an exciting and unexpected development.  

Having seen this, I immediately when down to the fridge for another Tortilla-Board™. As luck would have it, I was out of standard flour tortillas. We did have some sun-dried tomato and habanero pepper flavored tortillas from Trader Joes over in Bellevue. I grabbed one of these, and built another circuit to power the laser diode. I built a small power regulator to insure a steady signal level from my laser diode. The diode shoots a laser beam across the street forming a breakbeam sensor for the cars. The last two parts to insert onto the sun-dried tomato and habanero pepper Tortilla-Board™ were the connectors for the power.  I used a gold plated and a tin plated connector. Imagine my surprise when the power supply sprang to life on its own. The dis-similar metals between the connectors, in conjuction with the acids in the habanero peppers, created a 3.3 volt power supply. This is a truely powerful feature of the Tortilla-Board™ that shouldn't be overlooked.


Summary

The Tortilla-Board™ is a very viable and handy platform for experimenting with electronics. Assembly is easy, availability is as close as the grocer, and they are 100% bio-degradable. I highly recommend that you try a Tortilla-Board™ for your next project. It is a safe, clean, and tasty way to construct your wildest projects.